Field of Invention
The present invention relates to a field of sludge reduction treatment, and more particularly to a radial flow hydrothermal reactor for a sludge thermal hydrolysis treatment.
Description of Related Arts
The municipal sludge is the by-product of the municipal sewage treatment, and a general name for the small amount of sediment, particles, and floats, generated by treating the municipal sewage with the conventional method. The municipal sludge has the following characteristics.
(1) High Production and Low Harmless Treatment Rate
The annual production of the sludge is 28 million tons (water content of 80%, in 2011), and three quarters of the sludge is not effectively treated.
(2) High Water Content and Dewatering Difficulty
The conventional mechanical dewatering method for the sludge merely reduces the water content of the sludge to about 80%.
(3) Harmfulness and Usefulness
Various organic pollutants and heavy metals exist in the municipal sludge and are harmful to the environment if being directly discharged. However, the municipal sludge has the high calorific value (7500-15000 kJ/kg dry sludge) which can be utilized as resources.
Currently, the most common sludge treatment methods are composting, landfill, and incineration, but the three methods have the requirements on the water content of the sludge. For example, the sludge landfill requires the water content of the sludge to be lower than 60%; for the sludge composting, it is required to add the bulking agent to adjust the water content to about 50%; and, for the sludge incineration, it is required to reduce the water content of the sludge to about 30%. Thus, it is necessary to further dewater the wet sludge having the water content of about 80%.
It is feasible to further dewater the sludge through the thermal drying method. The thermal drying method is able to reduce the water content of the sludge to lower than 50%, with a good reduction effect and stable product. However, the thermal drying method has the problems of the high technical requirements, the relatively complex management, the high energy consumption, and the relatively high treatment cost. In order to evaporate a ton of water, the sludge thermal drying method consumes 887025 kcal calories, namely 107 m3 of natural gas which has the calorific value of 8300 kcal/m3. For example, in order to reduce the water content of the wet sludge from 80% to 10% through the thermal drying method, each ton of the dry sludge consumes about 428 m3 of natural gas and 300 kW·h electricity. The drying cost of each ton of the dry sludge reaches 1144.9 yuan (without considering the personnel salary and the device depreciation). It is easy to establish the thermal drying device, while it is too expensive to use. Thus, it is urgent to provide an economical method to replace the conventional thermal drying method.
The sludge hydrothermal treatment technology is to heat the sludge, and hydrolyze the viscous organics in the sludge at a certain temperature and pressure, so as to destroy the colloidal structure of the sludge and improve the dewaterability and the anaerobic digestion performance. The hydrothermal treatment technology is also called the thermal conditioning. According to whether the oxidizing agent is added during the hydrothermal treatment, the hydrothermal treatment technology is divided into the thermal hydrolysis and the wet oxidation. For the thermal hydrolysis, the oxidizing agent is unnecessary; for the wet oxidation, it is necessary to introduce the oxidizing agent into the reactor.
The sludge thermal hydrolysis technology is able to further reduce the water content of the sludge, high-effectively and economically. During heating the sludge, the microbial flocs in the sludge are dispersed; the microbial cells are broken; and the organics in the sludge are hydrolyzed, causing a decrease of the sludge viscosity and the water-holding capacity of the viscous materials to water. Moreover, when the sludge is heated to a certain temperature, the cells of the organics in the sludge are broken; the macromolecular organics in the cells are released and hydrolyzed; and the water bound with the various macromolecules in the cells is also released, causing an easier separation of the water from the sludge particles, which realizes the sludge dewatering and drying with the low energy-consumption and the high efficiency.
The hydrothermal reactor is the core device of the sludge thermal hydrolysis technology. However, the conventional hydrothermal reactor has the problems of the insufficient reaction, the poor continuity, the incompact structure and the large occupied area.